The majority of cluster mills for cold rolling metal strip have been provided with monobloc housings of the type shown in U.S. Pat. Nos. 2,169,711; 2,187,250 and 2,776,586 or the improved type taught in U.S. Pat. No. 3,815,401 and also illustrated in FIGS. 1a and 1b herein.
The advantage of the monobloc housing over any other housing type is great rigidity which is required in order to roll strip having the greatest uniformity in thickness. It will be noted by one skilled in the art that, as time progresses, requirements for gauge accuracy (i.e. thickness uniformity) are becoming increasingly stringent.
However, there are some disadvantages with respect to the monobloc housing, which, for some applications, can cause serious difficulties. These disadvantages can be summarized as follows:
Firstly, if a mill wreck occurs, i.e. the strip breaks and then accumulates in a tangled mass of scrap inside the housing, it sometimes takes several hours to remove the tangled strip, to enable rolling to recommence, and so significant lost production occurs. It would be advantageous in such cases to be able to separate upper and lower halves of the housing to provide more room for removal of scrap strip. This is particularly important for high speed mills.
Secondly, for some applications, it would be advantageous to be able to roll with a larger range of work roll diameters than can be achieved with a monobloc housing.
Thirdly, the ability to separate upper and lower halves of the housing would facilitate threading of the strip.
Fourthly, the ability to mount force measuring devices between upper and lower halves of the housing would enable more accurate measurement of roll separating force, which could be useful for purposes of data logging and improving accuracy of automatic gauge control systems.
Prior art alternative housing designs have overcome all of the difficulties, but paid the penalty of a great reduction in mill rigidity. Some examples of such prior art are shown in FIGS. 2, 3a and 3b of U.S. Pat. No. 5,596,899.
These housings are discussed in the above-noted co-pending application. The above-noted co-pending application, the teachings of which are incorporated herein by reference, discloses a housing that, although overcoming all of the difficulties mentioned above, includes both screws and prestressing cylinders and so would be too expensive for some applications.
It is the object of the present invention to provide a housing for a cluster mill having all the advantages of prior art split housings, while maintaining a housing stiffness almost as high as that of a monobloc housing, and without requiring the use of costly prestressing elements.